Reland remaining bits of "Upconvert various types to int."

Reland remaining bits of "Upconvert various types to int."

Most of commit cb180976dd0e9672cde4523d87b5f4857478b5e9 (which reverted
commit 83ad33a8aed1fb00e422b6abd33c3e8942821c24) was already re-landed.  This relands the rest, including modifications by kwiberg to hopefully avoid regressing performance.

In a subsequent change I will see if removing the int16_t cast in this modified version still causes perf problems.

BUG=499241
TEST=none
TBR=andrew

Committed: https://crrev.com/72cfd6c468663a95962d2677c94d91d97b71f980
Cr-Commit-Position: refs/heads/master@{#9487}

[Peter Kasting, 2015-06-12 03:26:22]

pkasting@chromium.org changed reviewers:
+ andrew@webrtc.org

[Peter Kasting, 2015-06-23 01:26:23]

The CQ bit was checked by pkasting@chromium.org

[commit-bot: I haz the power, 2015-06-23 01:26:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1181693005/40001

[commit-bot: I haz the power, 2015-06-23 02:33:55]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-06-23 02:34:08]

Patchset 3 (id:??) landed as
https://crrev.com/72cfd6c468663a95962d2677c94d91d97b71f980
Cr-Commit-Position: refs/heads/master@{#9487}